<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
          width: 200px;
          height: 200px;
          background-color: red;
          /* 固定位置 参照物：窗口 */
          position: fixed;
          right: 0;
          bottom: 0;
        }

        p{
          height: 1000px;
        }
        .p1{
          background-color: aqua;
        }
        .p2{
          position: relative;
          z-index: 1;
          background-color: gold;
        }
        .p3{
          background-color: hotpink;
        }
      </style>
</head>
<body>
    <div></div>
    <p class="p1"></p>
    <p class="p2"></p>
    <p class="p3"></p>
</body>
</html>